The present invention relates to a surveying system, in particular, the invention relates to a surveying system for tracking a target.
As a surveying device for measuring a distance, a horizontal angle and a vertical angle, a surveying device provided with a tracking function has been known in the past. In this type of the surveying device, an object reflector (target) such as a corner cube is collimated by a collimating telescope provided on the surveying device. A tracking light is projected from the collimating telescope, and when the target is moved, a reflection light from the target is received and the target can be automatically tracked.
Normally, in the surveying device provided with the tracking function, no operator is assigned on a side where the surveying device is installed and a surveying operator carried out an operation on a side of the target. For instance, a target installed on a pole or the like is held by the surveying operator, and the operation is carried out by a remote controller. Also, the target is moved by the surveying operator for each measuring point, and in the surveying device, the target is tracked by detecting a reflection light from the target.
Or, the target is installed on a pole erected at a required position on a construction machine such as a bulldozer. The operator operates the construction machine such as a bulldozer, and operation such as ground leveling is carried out by the construction machine based on a reference plane formed by the surveying device or based on the results obtained by the measurement. The surveying device tracks the target in association with the movement of the construction machine.
However, when the moving speed of the target exceeds the following speed of the surveying device and the target moves out of a visual field of the collimating telescope or when an obstacle such as a tree, a vehicle, a person, etc. is temporarily positioned between the surveying device and the target and an optical path of the collimating telescope is intercepted by the obstacle, the surveying device cannot receive a reflection light from the target, and a tracking may be interrupted.
The reason for this is that, in a collimating telescope generally in use, a field angle (an angle of view) is as small as about 1° and the reason is caused by that the range to detect the reflection light for purpose of tracking is too narrow.
When the tracking of the target is interrupted, the surveying device starts the operation to search the target. In the searching operation, the collimating telescope is rotated within a predetermined range in up-to-bottom direction and in left-to-right direction while the tracking light is projected, a scanning is carried out, and the target is detected.
As described above, the field angle of the collimating telescope is small. In order to re-detect the target, it is necessary to have a finer scanning pitch and to increase the number of scanning operations.
For this reason, when the tracking is interrupted, much time is required for the purpose of detecting the target again and for starting the tracking operation. Further, under working conditions where the optical path is frequently intercepted by the obstacle, there are problems in that the working efficiency of the measurement operation is extremely decreased.
The surveying device provided with the tracking function is disclosed in JP-A-07-198383, JP-A-2000-346645, and JP-A-2004-170354.